Soil moisture control system and method

Abstract

Soil moisture control system senses subsoil moisture by AC conductivity and turns on irrigation valve when the sensor indicates the need for additional moisture. An adjustment is connected to the sensor to adjust the level at which adequate soil moisture is signaled.

What is claimed is: 
     
       1. A soil moisture control system comprising: an alternating current source for supplying alternating current;   a switch and a magnetic coil serially connected to said alternating current source, said magnetic coil being for connection to an irrigation water valve so as to control the opening and closing of the water valve;   a soil moisture sensor having first and second spaced electrically conductive graphite rods forming probes for sensing the moisture in soil between said probes, first and second resilient metal springs wrapped around the cut into said first and second graphite rod probes, respectively, said first and second metal springs being connected to said alternating current source so that alternating current passes between said probes when said sensor is immersed in moist soil, said sensor being connected to control said switch; and   including a gate circuit connected to said switch for controlling said switch and said soil moisture sensor being connected to said gate circuit so that said switch changes states when said sensor detects a predetermined amount of moisture in the soil between said probes so that said soil moisture control system inhibits delivery of irrigation water to the soil when soil moisture is adequate.   
     
     
       2. The soil moisture control system of claim 1 wherein said gate circuit is adjustable so that change of state of said switch can be adjusted in accordance with desired soil moisture content. 
     
     
       3. The soil moisture control system of claim 2 wherein said switch is a triac having two terminals and a gate and said sensor is connected between one of said terminals and said gate of said triac. 
     
     
       4. The soil moisture control system of claim 2 wherein said adjustable gate circuit can be adjusted so that said sensor always indicates the need for sprinkling. 
     
     
       5. A soil moisture control system comprising: an alternating current source for supplying alternating current;   a switch and a magnetic relay coil connected to actuate relay contacts which control the flow of power to the solenoid of a water control valve so as to control the opening and closing of said water valve;   a soil moisture sensor having first and second spaced electrically conductive graphite rods forming probes for sensing the moisture in soil between said probes, first and second resilient metal springs wrapped around and cut into said first and second graphite rods probes, respectively, said first and second metal springs being connected to said alternating current source so that alternating current passes between said probes when said sensor is immersed in moist soil, said sensor being connected to control said switch; and   a gate circuit connected to said switch for controlling said switch, said gate circuit comprising a triac having one of its main terminals connected through a variable resistor to said first probe and having its gate connected to said second probe and having its main terminals connected to actuate said switch so that said switch changes states when said sensor detects a predetermined amount of moisture in the soil between said probes so that said soil moisture control system inhibits delivery of irrigation water to the soil when soil moisture is adequate.   
     
     
       6. The soil moisture control system of claim 5 wherein said coil of said water control valve is connected between a first bus connected to said alternating current source and a second bus connected to a clock. 
     
     
       7. The soil moisture control system of claim 5 wherein said relay coil is connected to the output of a rectifier, the input of said rectifier being connected to said switch so that said sensor controls said switch, said switch powers said rectifier and said rectifier powers said coil. 
     
     
       8. The soil moisture control system of claim 6 wherein said gate circuit is adjustable so that change of state of said switch can be adjusted in accordance with desired soil moisture content. 
     
     
       9. The soil mixture control system of claim 8 wherein said adjustable gate circuit can be adjusted so that said sensor always indicates the need for sprinkling. 
     
     
       10. The method of control of irrigation water comprising the steps of: preparing a ground moisture sensor having first and second spaced carbon rod probes and making electrical contact with the carbon rod probes by wrapping a separate metallic spring around each of the probes so as to cut into the carbon rod probes;   inserting sensor having the first and second spaced probes into soil in which moisture is to be sensed;   applying alternating current across said spaced carbon probes through the contact springs;   measuring current so that when the current between the probes changes across a critical value a signal is emitted; and   controlling a sprinkler valve in response to the emitted signal.   
     
     
       11. The soil moisture control method of claim 10 further including the step of adjusting the voltage applied to the probe so that the transition point is adjusted with respect to soil moisture. 
     
     
       12. The soil moisture control method of claim 11 wherein the step of signaling the transition includes the step of signaling a relay and the further step of signaling to the water control valve from the relay.